Tunnel kiln



NOV. 18, 1952 E VAN DER PYL 2,618,671

TUNNEL KILN EDH/4R0 l/A/V DEE PVL Nov. 18, 1952 Filed Jan. 18. 1949 400 4/0 40? 5y af/FV# A Trae/yay NOV. V18, 1952 E, VAN DER PYL, 2,618,671

TUNNEL KILN Filed Jan. 18, 1949 3 Sheets-Sheet 3 Patented Nov. 18, 1952 UNITED STATES PATENT OFFICE TUNNEL KILN kEdward Van Yder Ryl, Holden, Mass., assignor `'to 4Norton Company, Worcester, Mass., a corporation of Massachusetts Cl. 1li-.20)

8 Claims.

The invention Vrelates to tunnel kilns.

One .object of the invention .iis to provide a tunnel kiln particularly adapted Afor vitrifying large Lmassive Apieces such as pulpstone blocks or segments. .Another object of the invention is to provide :a tunnel :kiln particularly :adapted for `vlitr'ifyingllarge:pieces of warewhich are thickin vevery dimension.

l.Another object of the yinvention is to provide :an electric tunnel kiln which delivers radiant energy at the top, bottom and lboth sides of .the tunnel. Another object of thepinvention iis .to

provide a construction Jfor a tunnel kiln having 'electrical resistor rods `:both 'horizontally and'veritically A.thro-ugh rthe tunnel. Another .object of 'the invention is to place four :banks of resistor rods as close as possible to the'ware being vitrified fbothvabove, below and on each side of itheware in 'the tunnel of a kiln, thus lgreatly 4accelerating 'the zvi'tricationzof .massive pieces of ware. Anfothenobjectoi fthe invention is greatly to accelerate the yvitritlcation of large massive pieces of warevsuch as'pulpstone blocks. Another object of the inventionlis to provide a tunnel kiln capable fof vi-trifyin'ga relatively large mass vof ware .per yea-r :as .compared with .the mass of thekiln.

Another object .of the-invention is to provide transportation :meanstfor Ware through atunnel V.kiln of unique :characteristics in vthat only batts need-be used and except .in the `iiring zone and adjacent thereto anti-friction devices are employed, butin the iiiring :zone Athere is t-nothing but refractory material, no metal parts Y'being present in th'enringzone.

Aother'objects'vvill be in part obviousfor inzpart pointed out hereinafter.

iIn the accompanying Vdrawings illustrating one yofrnasny possible 'embodiments of the mechanical Afeaturesfofthis invention,

Figure I1 Tis 1a side elevation fof the kiln on 'a irelduced scale.

EignreZ is a side elevationof the .ring zone of the 4kiln-on fa-scaile larger than that :of .Figure l.

`Figures 3 and 4 are vcross sectional views taken respectively on the lines 33 and V4--4 `of Figure 2, lbutfshowin'g the parts one, largerscale.

Figuresl, .=6 andi?. are cross sectional views on thesame-scale Aas Figures 3 and 4, and taken on the lines -=5,1'66 `and'l--Z'I respectivelyof Figmiel.

l`The kiln as a whole is identified by the numeral and comprises a steel -box having the shape of a .parallelepiped This -steel boxand its contents :areisupportedby legs 2|. A-t the entrance-end yof :theikiln there is a Afront Wall 3'0 comprising a large piece of steel plate. /At the `exit end of the kiln 'there is a similar rear lwall 32. Extending through vthekiln from end to end, that is from `theft-ront wall 30' to the rear wall '32, isa long tunnelSB. 'To operate vthe vkiln a great number -of rest upon the side bricks batts"areprovidedfand these batts 80 may 'have the :shape shown in Figures 3 to '7 inclusive. There isarkiln'bot'tom 400 andra kiln top 40| and both .o'f these may 'be madefof steel plate. There are kiln side walls 402 and these likewise may be made of steelplate.

VThe legs 2| are each formed of la pair of angle irons Which extend all the Way to .the top Aof the 'kiln'thus -,bracing `the side Walls 402. Additional vertical angle irons 4`04'may beprovided between the legs 2| to 'furnish further bracing. On each Aside of Ithe kiln `there is a long series of longi- :tudinal irons "405 at an upper level anda short .series of longitudinal irons 406 .at .a lower level. ,At Ithe firing vzone of the kiln are short Vertical angle Airon braces '407. ,Across the top of the :kiln are .angle iron :braces 408 andacross the bot- -tom 'of the kiln fareangle iron braces 409.

This entire .metal structure is ,preferably held :together by Welding and constitutes la strongbox. Itis preferably rectangular in any cross section fbutzas will :be seen from rFigure 1 the side elevation is a non-rectangular parallelogram the angles at the end being slightly :more and less than namely about .2 more and less. 'Thus the 'entire Akiln y2i) -is inclined downwardly at va lslight inclination from the .front wall 30 to the rear Wal1'3'2zand this is ymore 'particularly to -pro- Videla slightrdraughtiin'the tunnel 135 of the kiln. Therefore the sectional views Figures 3 to 7 are .not -quite 'ver-tical sectional views being at an inoline iof :about the 'same 2 to the vertical. In constructing the :refractory structure now .about to be described, .rectangular parallelepipedal bricks are usedand fthe supporting bottom level of bricks 4|-0 are placed with side faces thereof rightfon the -ki-ln bottom 400.

llhe vrefractory structure of the kiln lcomprises .this `bottom level 'of bricks 4|0 herein shown as one kbrick high, side walls of bricks 4| a kiln bottom structure 4|2 which may -be three bricks high .as shown, and, except where out away as will hereinafter appear, is a parallelepiped, courses `of tunnel Vside bricks 4|3 shown in each section 4as one brick on each side, -courses vof upended bricks 4|`4 adjacent the walls 4| l, there being'one brick`4|4 on each side at any section, "tunnel arch bricks M5, one at every section, .between kthe courses 4 |4, and a parallelepipedal kiln top layer of bricks 4|6'between the walls 4| and rabove the Jcourses 4|4 and the 'tunnel arch bricks 4|5. This parallelepipeda'l kiln'top layer '41.6 may ybe two 'bricks high 'as shown. The tunnel arch bricks l415 form the tcp of the Vtunnel '35 and they '4|3 vwhich as shown form the rsides of the tunnel 35, and the bottom of the tunnel t35 'is formed by the 'kiln bottom s-tructuref4|2.

Between the steel side walls '402 Yand the 'brick fside walls 4|.`| vvon leach side is loose refractory material 423 as further heat insulation. This loose refractory material 420 is also preferably placed between the kiln 'top layer of bricks 4|6 and the kiln top 45|. A material which is very Satisfactory to use for this loose filling is finely divided diatomaceous earth which has high thermal resistance.

Referring now to Figure l, it is convenient to describe the kiln 23 as divided into bays, each bay having the volume of kiln bounded on one end by the plane of a pair of legs 2 l, one on each side and on the other end by the plane of an adjacent pair of legs 2|. Half a bay is described as the volume of the kiln bounded by the plane of `a pair of legs 2| and the plane of a pair of vertical angle irons 444 or angle iron braces 441. The foregoing is merely for convenience in referring to various parts of the kiln because there is no boundary line between bays or half bays in the tunnel 35 and some bricks may be partly in one bay and partly in another bay.

. Referring now to Figures 3 to '7 inclusive, extending the entire length of the tunnel 35 are parallel refractory members 42|, there being a continuous succession of these members 42| on each side of the tunnel 35 and each succession of members 42| extending without a break from the entrance end to the exit end of the tunnel 35.

vThese refractory members 42| are preferably made of self-bonded aluminum oxide and they are thus highly refractory and resistant to Wear. Located in the grooves in these members 42| are rods 425 which are also preferably made of selfbonded aluminum oxide and therefore also are highly refractory and resistant to wear. There is a continuous succession of rods 425 on each side of the tunnel 35 and the rods 425 are in contact With each other. These rods 425 are cylindrical but their ends are tapered. The batts 8G, Which are preferably made of vitried silicon carbide, also a very refractory material, ride upon these rods 425 in the hotter bays. We have found that silicon carbide batts riding upon aluminum oxide rods is a highly practical answer to the problem of moving material to be vitried through the firing zone of a kiln for the rods 425 and the batts 80 can withstand temperatures above 1300 C. in an oxidizing atmosphere during repeated cycles and furthermore are resistant to heat shock, and both parts are resistant to Wear and Figure 1: bay No. bay No. bay No. 8 andi the first half of bay No, 9 which is the nal bay. It will be seen that bay No. 3 and bay No. 4 are the firing zone bays; bay No. `and bay No. 2 are the preheating zone bays, but bay No. 2 is quite close to the firing zone so there are no channel irons 432 and rollers 430 in bay No. 2. Similarly bays Nos. 5 and 6 are annealing zone bays but they are also so close to the firing zone that no channel irons 432 with rollers 430 are placed therein. The remainder of the annealing zone comprises bays 1, 8 and 9 and the channel irons 432 with rollers 43|) can be placed the entire length of this part of the annealing zone but there is an advantage in omitting them in the 4 nal half bay of the kiln which will presently be explained.

In order that the rollers 430 may support the batts 84, the rods 425 which are alongside of rollers 430 are undersized rods. For example the rods 425 wherever there are no rollers 430 may be Y 11/4" in diameter .and the rods 425 where there are rollers 430 may be only 1 in diameter. The rollers 430 are of such height that they support the batts above the tunnel bottom at the same height as do the full diameter rods 425. It will be noted that the rods 425 are located under grooved enlarged marginal portions 435 of the batts 80 whereas the rollers 434 are located just inside these grooved enlarged marginal portions 435. The channel irons 432 are just inside of the refractory members 42| and a continuous set of channel irons 432 on one side is parallel to a continuous set of channel irons 432 on the other side. Thus the refractory members 42| extend from end to end of the tunnel 35 but the channel irons 432 and rollers 430 are found onlyin bay bay l, bay 8 and the rst half of bay 9. In the last half of bay 9 the rods 425 are full size and support the batts 80 and the reason for this is that if the batts 8|] at the exit end of the kiln were supported by rollers 435, there would be nothing to stop the motion of the batts once started especially in view of the slight downgrade, so to hold the batts in the annealing zone of the tunnel a frictional brake is applied to them in the final half bay thereof.

The reason for providing rods 425 supported by members 42| in those bays where there are channel irons 432 With rollers 430 is that thereby a Whole line of rods 425 can be removed from the kiln merely by pushing them, thus to replace rods 425 when finally they become worn too much. Also in this manner the rods can be rotated from time to time to distribute the Wear merely by removing them and replacing them. Therefore undersized rods are provided where the rollers support the batts and everywhere there are rollers 430 there should be undersized rods 425 but wherever there are no rollers 434, the rods 425 should be of full size. The reason Why the ends of the rods 425 are tapered is so that a batt 80 can ride across a rod junction without catching.

For the bricks 4| and 4|6 inclusive any refractory material of adequate strength and thermal resistance may be used but I have found that a very satisfactory material is porous kaolin which makes a light weight brick that is therefore easy to handle, which makes a somewhat soft brick, which is therefore easy to cut, Which is suiiciently refractory to withstand a temperature of more than 1300 C., which has a high thermal resistance, and which is relatively inexpensive.

Referring now to Figures 2, 3 and 4, the firing zone of the kiln which comprises bays No. 3 and No. 4 in this embodiment of the invention has two banks of rod resistors 440 extending horizontally through the kiln and two banks of rod resistors 440 extending vertically `through the kiln. The horizontal rod resistors 440 pass through refractory bushings 44| which extend from the outside of the wall 402 to the outside of the wall 4| on each side of the kiln; the vertical rod resistors 448 pass through refractory bushings 442 which extend from the outside of the kiln top 44| through the material 442 to the top of ythe bricks of the kiln top 4|G, and at the bottom these vertical rods 443 pass through refractory bushings 443 that extend from the underside of the kiln bottom 400 to the topof the supporting .bottom .level of :bricks .4110. .From the :bushings .44:1 @at oneside to the bushings 41111v at the .other side fthe upper bank of horizontal rods --440 extend .through .the sidewalls 14.11, the 4upv.ended .-bricks4i'1i4, and .each .one .extends through one Itunnel y.arch brick4i1f5. Comp'aringinow Figures 3 and 4 with Figure Y5 for 4exa-rnple,.it will be seen .that :the tunnel farch :bricks 4.15` in the --ring `zone have .ceilingwaults-'44'5 permitting .a .length 'of '.eachhorizontal rod resistor 440 :of `the upper bank toV extend rclear `of the brick 'work '-:a-nd 'thus to heat the z-tunne1i355at .theiring zone by direct radiation. Likewise comparing Figures 3,4 :and .5, fit `will vbe -seen v.that in Athe firing `zone ings 44-1-on the other side, 4through the walls 411 A'and the vkiln bottom structure 41.2 and across this floor :trench 446 `wherethey provide direct radia- Vtionin the tunnel 35 especially-to the underside .-of the batts 8B.

The vertical rod resistors 440 extend in parallel banks, one on each side of the tunnel 35, from the bushings v443 at the bottom through the kiln lbottom structure v412, then through embra- `.sures 441 formed bycutting away the Vcourses of ,side bricks 413 in the firing zone, -then the rods 44.0 extend upwardly through the tunnel larch bricks 415 and through the kiln top 416 to the upper bushings 442. rSo that the vertic-al rods 440 will not drop out of the kiln they yare supported by brackets 450 attached to the kiln bottom 4130 and insulating ,pads 451 are provided to vpreventshort circuiting of the rods440.

These .rod resistors-44 :may .be of any type `capable Aof being heated .to 'a temperature of .above '140W C.l by the passage 4of electric cur- -rent therethroughand having a reasonable life at suchiternperatures or, incase ware of less refractory characteristics than the usual grinding Wheel is to be vitried in the kiln, the rods 440 might be of a type ,capable of being heated only to lower temperatures. For vitrifyi-ng grinding wheels and pulpstone blocks and the like the vbestrod resis-tors nowknown to me .are silicon carbide resistor rods. crystallized silicon carbide and they .are cold ended, that is they have cold ends .of low resistance. For example, silicon Acarbide fines .of several different grit sizes and of the purer grades are mixed with asmall quantity of so'- 1 'dium `silicate then Vthis material is tamped into an iron pipe lined ywith paper and having holes yin its w-all, then the pipe is placed in an oven to Vdrive 01T the water'fiom the sodium silicate, the baked rod of bonded silicon carbide is removed and-itis then recrystallized by passing electric r-current -through it and, in certain cases, itmay -begiven -a `'further heat treatment at the recrystallizing temperature in an induction tube furnace .made of graphite. Later on the rod isr-coldrended v'by .causing superheated liquid siliconto permeate -the pores .of the end portions.

I.the bottom `4111), the top 40.1 or .near the sides These are made of re- 402. It Ywill thus Vbe `seen that the 4heat provided .by the electrical resistor rods 441Jiis liberatedal- .most entirely .in the vault 445, in the trench446 and inthe embrasures 441.

The rod resistors .440 are connectedA to .electric power .in :a .manner well known `:to 'those skilled in the yart, Asoenodiagram of the yelectric: circuits nor description 'thereof need be Aprovided herein. The rodtresistorsshould be :electrically heated'to a high 'enough "temperature rso .that the :ring zone of the'kiln (bays -3 and 4) will be at vitrlfying .temperature to vitrify the particular ware involved. In the 1case of large pulpstone'blocks V'451) this temperature should :be of the order of 1200 C. or 1300 -C. in Athe ring zone in the tunnel -E15. From "Figures 3 .and4 it will beseen that the rods l4411 radiate heat directly upon the top and lupon thesides of the blocks 45D `and the lower bank Yof horizontal rods V4411 radiate heat vdirectly '.tothebottoms of the batts 80. The batts are thin and silicon carbide is a goodheat conductor, so -the blocks 450 are heated from four sides by direct radiation and thus the heat Apenetrates evenly. The vitriiication of massive pieces of ware `such 4as the blocks 4450 has .always Ybeen a problem and in conventional kilns :has takenseveral days. With the kiln of this invention llarge pulpstone blocks 450 can be vitriiied in ten hours counting from the time -a cold block 1455 a green state is rammed into the tunnel Atby a Vram, not shown, to the Vtime it emerges from Ythe tunnel 35 fully vitrified.

In order that the operator of the kiln may have knowledge of the temperature of the -various bays-of the kiln in the tunnel 35, pyrometers may be provided at intervals along the kiln 20 but it hasrnot been thought necessary to show `these in the drawings. The operator vcan change the temperature in the firing zone or parts thereof by adjusting the-current flow to the rods 440 or .to A`particular' groups thereof, all in la vmanner well knownand automatic controls maybe providedflif desired. The temperatures of the various bays of the preheating and annealing zones can be controlled by the-operator by means of various dampers in flues as will now be described.

The green pulpstone blocks 450 or other ware usually contain combustible organic material as a temporary binder; this starts vaporizing even as early as bay No. 1 and burns in subsequent bays of the preheating zone yand finally becomes completely burned out at-'some point in the firing zone and vtherefore it is desirable to carry off the gases vproduced by this material and especially to provide enough oxygen so that little if any carbon residue will remain. So therefore the kiln 20 is provided `with a chimney v455 and this, as shown in Figure 6, is connected to a chimney flue 456 which is integral with a pair of flues 451 extending from the ilue 455 at first angularly and then istraight downward to a level below the bottom of the tunnel 35, there being vone flue 451 on each side of the kiln. These flues 456 and 451 may be built into one piece out of refractory sheet metal such as a nickel-iron-chromium alloy of 50 nickel, 24`iron and 16 chromium, inserted in place after certain bricks have been .laid vsome of these being cut, and thereafter the other bricks are suitably cut and laid around and inside of the flues 451 as shown in Figure 6.

Also made of the same sheet metal and connected to the flues 451 are horizontal connecting passages 458 extending above cut tunnel side wall bricks 413 Vto the inside of the tunnel 35. These passages 458 collect the gases in the tunnel 35 to the fiues 451. The iiues 451 at the bottom extend right out to and through the walls 402 of the kiln and are closed by removable plates 461. Removal of the plates 46| allows easy access to the inside of the tunnel 35 for any purpose. There are `also removable plates 462 on the sides of the kiln as shown in Figure l-inside of these plates the bricks may be shaped for ready removal, also for access to the inside of the tunnel 35 in various bays. Such access is desirable in case of a smash in the tunnel which, however, rarely occurs.

Referring now to Figure 7, a flue 465 is connected to flues 466 which extend over and down the sides of the kiln and are connected to transverse passages 461 and 468. The flues 466 form a U as shown and they as well as the passages 461 and 468 can be made of sheet steel because the temperature at this part of the kiln is not so high. The passages 461 extend through the side walls 402, the side walls 4l l, and the side bricks 413 to the tunnel 35 above the rods 425. The passagesl 468 extend through the side walls 402, the side walls 4I| and the kiln bottom structure 412 and are connected to a well 460 in the bottom of the tunnel 35. As shown in Figure 1, I provide slide dampers 41D and 41| to control the amount of air flowing from the upper part of the tunnel 35 and from the lower part of the tunnel 35 respectively into the ilues 466.

The flue 465 is shown in Figure 1 and connects the ues 466 to the flue 456 and so to the chimney 455. There is preferably a slide damper 412 in the flue 456 to control the amount of gases going up the flues 451 and a rotatable damper 413 in the chimney for overall control. and passages 461 and 468 constitute back draught means so that the suction created by the heat in the tunnel and the stack effect of the chimney 455 can be prevented from drawing too much air along the tunnel 35 in the annealing zone. There should be a small ow of air into the preheating zone of the kiln, preferably moving into bay No.

2, to provide oxygen for burning out the organic `found that the organic matter in the green" ware provides, in burning a significant amount of heat. It is desired that this organic matter be burned rather than merely volatilized in order to eliminate carbon deposit in the ware.

So far as the present invention is concerned, the batts may be propelled through the tunnel continuously at slow speed or intermittently by ramming a batt 8U or two or more batts 8D at a time into the tunnel 35, but at infrequent intervals, and any suitable mechanism may be used for this purpose. Automatic batt feeding and discharging mechanism for ramming batts from time to time into the tunnel 35 at the front wall 36 and removing them from the exit end of the kiln at the wall 32 is disclosed in a copending application filed by myself and George N. Jeppson on May 10, 1947, Serial No. 747,169, now Patent No. 2,523,025, granted September '19, 1950, and this mechanism may be profitably used with the kiln of this invention or an improvement The flues 465, 466 f thereon disclosed in a copending application filed by myself and George N. Jeppson on January 28. 1949, Serial No. 73,312, may likewise be used.

It will thus be seen that there has been provided by this invention a tunnel kiln in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. Y

I claim:

1. A. tunnel kiln comprising refractory bricks forming a structure which has one dimension of great length compared with others and forms a tunnel which has a vault in the top, a trench in the bottom and a pair of embrasures at the sides, said vault, said trench and said embrasures being located at the firing zone of the tunnel, a pair of sets of stationary parallel refractory rods in said tunnel located, in said firing zone, above said trench, below said vault and inside of said embrasures, a continuous shelf of refractory batts resting on said rods and slidable thereon, and silicon carbide electrical rod resistors in the vault, in the trench and in each of the embrasures the silicon carbide resistors in the embrasures extending completely through the kiln from the top to the bottom thereof, whereby a ram can propel the batts in a long line of batts on the refractory rods through said tunnel and between said electrical rod resistors.

2. In a kiln, a refractory structure forming a long tunnel having, in a firing zone thereof, a. vault in the top, a trench in the bottom and a pair of embrasures in the sides, a refractory support in said tunnel comprising a pair of sets of stationary refractory rods each set being parallel to the other set and there being a substantial space between the sets and the rods being located above the trench, below the vault and between the embrasures, silicon carbide electrical rod resistors in the vault, in the trench and in the embrasures the silicon carbide resistors in the embrasures extending completely through the kiln from the top to the bottom thereof, the electrical rod resistors in the trench and in the embrasures being spaced from the refractory rods by a distance no greater than the distance between the se s.

3. In a tunnel kiln, a refractory structure forming a long tunnel having, in a heating zone spaced from the ends of the tunnel Va vault in the top, a trench in the bottom, and embrasures in the sides, a plurality of silicon carbide` electrical rod resistors extending through and across said ltunnel in the trench, a plurality of silicon carbide electrical rod resistors extending through and. across said tunnel in the vault, a plurality of silicon carbide electrical rod resistors extending from the top of the kiln to the bottom thereof through each of the embrasures, a straight stationary refractory rod support for batts on one side of the tunnel and extending through the heating zone above the trench, below the vault and adjacent one embrasure, a straight stationary refractory rod support for batts parallel to the rst named straight refractory rod support for batts located on the other side of the tunnel and also above the trench, below the vault and adjacent an embrasure, and refractory batts resting upon said supports slidable therealong.

4. A tunnel kiln comprising a refractory structure forming a long tunnel, a heating zone intermediate the ends of said tunnel said heating Zonev having a vault, a trench and a pair of embrasures and said heating zone having a plurality of silicon carbide electrical rod resistors extending through the trench, having another plurality of silicon carbide electrical rod resistors extending through the vault, each of said rod resistors in each of the trenches and the vault extending across the tunnel from side to side thereof, and said tunnel having a plurality of silicon carbide electrical rod resistors in each of said embrasures extending from the topl of the kiln to the bottom thereof, and said heating zone having stationary refractory batt supporting members in the lower part of said tunnel just above the plurality of electrical rod resistors in the trench, said batt supporting members extending lengthwise of the tunnel on either side thereof adjacent the embrasures and parallel to each other, refractory flat batts extending from end to end of the tunnel not only in the heating zone thereof but also in the other parts of said tunnel and, in the heating zone, being supported by the refractory supporting members, said batts therefore being above the plurality of electrical rod resistors in the trench and also being below the plurality of electrical rod resistors in the vault and there being a clear space between the rod resistors in the trench and the undersides of the batts, said tunnel being by the batts divided into an upper part and a lower part to reduce convection and provide for controlled heating and vitrication, the batts constituting supports for ware to be Vitried and there being a clear space in the heating zone from the top of the batts to the rod resistors in the vault whereby the ware is heated by direct radiation therefrom on the top and also by direct radiation to the underside of the batts and then through the batts, each batt exending across the tunnel from the refractory supporting` member on one side to the refractory supporting member on the other side, supporting members on the sides of the tunnel in the lower partl thereof in all portions of the tunnel outside of the heating zone, all of the supporting members being so located and positioned that the tops of the batts form a continuous plane from one end of the tunnel to the other end thereof, said batts being adapted to be moved through the tunnel by a ram.

5. In a tunnel kiln as claimed in claim 4, the combination with the parts and features therein specified, of refractory round rods constituting part of the refractory supporting members in the heating zone, and the batts having grooves in the underside thereof and resting upon said round refractory rods with the rods located in the grooves.

6. In a tunnel kiln as claimed in claim 5, the combination with the parts and features therein specified, of the further feature that the batts are made of silicon carbide and the refractory round rods are made of alumina.

7. A tunnel kiln comprising a refractory structure forming a long straight tunnel, said tunnel being divided into a preheating zone, a heating zone and an annealing Zone constituting parts of said tunnel in the order named from the entrance end to the exit end, said tunnel being further divided between top and bottom in all of said zones into an upper portion and a lower portion,

a continuous succession of flat refractory batts extending in a plane through all of said Zones and constituting the dividing means, a long line of supports for the batts on each side of the tunnel and weil above the bottom thereof, the supports in the heating zone including a pair of lines of stationary refractory cylindrical rods upon which the batts rest and slide, a vault in the upper portion of the heating zone, a trench in the lower portion of the heating zone, and ernbrasures in the heating zone on either side of the batts and the cylindrical rods upon which they rest and slide, a bank of silicon carbide electrical rod resistors in the vault extending across the upper portion, a bank of silicon carbide electrical rod resistors in the trench below the batts and extending across the lower portion, and banks of silicon carbide electrical rod resistors in the embrasures extending from the top of the kiln to the bottom thereof, said fiat refractory batts being adapted to be pushed through the tunnel by a ram.

8. A tunnel kiln comprising a refractory struce ture forming a long tunnel, said refractory structure having a groove from end to end of the tunnel on each side thereof in the lower part of the tunnel, said grooves being straight and parallel, a continuous succession of stationary rods in the grooves, said tunnel having a heating zone intermediate its ends, a set of rollers in straight end to end relation in portions of the tunnel outside of the heating zone alongside of the rods on one side, a second set of rollers in straight end to end relation also in portions of the tunnel outside of the heating zone alongside of the rods on the other side, said sets of rollers being parallel to each other, a continuous succession of fiat refractory batts in the tunnel extending Without gap between them from one end to the other end thereof and said batts being in a common plane, said batts being supported in the heating zone by the rods and some of the batts outside of the heating Zone being supported by the rollers, said rods in the heating zone being refractory.

EDWARD VAN DER PYL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 409,489 Nungesser Aug. 20, 1839 671,990 Diescher Apr. 16, 1901 1,335,199 Ruthenberg Mar. 30, 1920 1,495,503 Armstrong May 27, 1924 1,533,266 Reid Apr. 14, 1925 1,649,926 Ruckstahl Nov. 22, 1927 1,661,694 Fry Mar. 6, 1928 1,827,543 Robertson Oct. 13, 1931 2,034,721 Howe Mar. 24, 1936 2,290,551 Gier July 21, 1942 2,320,172 Brooke et al May 25, 1943 2,359,157 Roth Sept. 26, 1944 42,404,059 l-Iall July 16, 1946 2,465,137 Van Nordstrand Mar. 22, 1949 2,519,250 J eppson et al Aug. 15, 1950 2,523,025 Jeppson et al Sept. 19, 1950 2,534,518 Jeppson Dec. 19, 1950 2,577,935 Van der Pyl Dec. ll, 1951 FOREIGN PATENTS Number Country Date 802,598 France June 13, 1936 

